Kubernetes Environment Variables
Kubernetes Environment Variables
Environment Variables
Now, it is time to try the other metod of passing arguments, via environment variables.
From the kubectl run examples, we can see that environment variables can be set with the --env option.
pradeep@learnk8s$ kubectl run -h
Create and run a particular image in a pod.
Examples:
<SNIP>
# Start a hazelcast pod and set environment variables "DNS_DOMAIN=cluster" and "POD_NAMESPACE=default" in the
container
kubectl run hazelcast --image=hazelcast/hazelcast --env="DNS_DOMAIN=cluster" --env="POD_NAMESPACE=default"
<SNIP>
Let us redploy the same image kodekloud/webapp-color:v3 but this time changing the color of the app with environment variable.
pradeep@learnk8s$ kubectl run kodekloud-env-color --image=kodekloud/webapp-color:v3 --env=APP_COLOR=pink
pod/kodekloud-env-color created
pradeep@learnk8s$ kubectl get pods -o wide | grep env
kodekloud-env-color 1/1 Running 0 12s 10.244.1.30 k8s-m02 <none> <none>
pradeep@learnk8s$ minikube ssh -p k8s
_ _
_ _ ( ) ( )
___ ___ (_) ___ (_)| |/') _ _ | |_ __
/' _ ` _ `\| |/' _ `\| || , < ( ) ( )| '_`\ /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )( ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)
$ curl 10.244.1.30:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #be2edd;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-env-color!</h1>
<h2>
Application Version: v3
</h2>
</div>$ curl 10.244.1.30:8080/color
pink$
$ exit
logout
The curl tests confirm that the application is using the pink color now, which is passed with the environment variable, APP_COLOR.
If we look at the Pod description, Environment section, APP_COLOR: pink is seen as expected.
pradeep@learnk8s$ kubectl describe pod kodekloud-env-color
Name: kodekloud-env-color
Namespace: default
Priority: 0
Node: k8s-m02/192.168.177.30
Start Time: Tue, 15 Feb 2022 19:22:07 +0530
Labels: run=kodekloud-env-color
Annotations: <none>
Status: Running
IP: 10.244.1.30
IPs:
IP: 10.244.1.30
Containers:
kodekloud-env-color:
Container ID: docker://376016abd3ab8f65faa794cb746831f37c3ac16c0436598b08f9365bdd6176d4
Image: kodekloud/webapp-color:v3
Image ID: docker-pullable://kodekloud/webapp-color@sha256:3ecd19b1b85db381a0b6f78272458c3c274ac2a38e878d65700393899adb3177
Port: <none>
Host Port: <none>
State: Running
Started: Tue, 15 Feb 2022 19:22:08 +0530
Ready: True
Restart Count: 0
Environment:
APP_COLOR: pink
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-xj9jz (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
kube-api-access-xj9jz:
Type: Projected (a volume that contains injected data from multiple sources)
TokenExpirationSeconds: 3607
ConfigMapName: kube-root-ca.crt
ConfigMapOptional: <nil>
DownwardAPI: true
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 2m26s default-scheduler Successfully assigned default/kodekloud-env-color to k8s-m02
Normal Pulled 2m25s kubelet Container image "kodekloud/webapp-color:v3" already present on machine
Normal Created 2m25s kubelet Created container kodekloud-env-color
Normal Started 2m25s kubelet Started container kodekloud-env-color
Save the current running pod as a YAML file.
pradeep@learnk8s$ kubectl get pods kodekloud-env-color -o yaml > pod-env-variable.yaml
As this is a running Pod, the YAML output shows a lot of other details on Status, which is not required for now (to change the environment variable).
pradeep@learnk8s$ cat pod-env-variable.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: "2022-02-15T13:52:07Z"
labels:
run: kodekloud-env-color
name: kodekloud-env-color
namespace: default
resourceVersion: "15077"
uid: bd7c01ae-553e-4f77-b589-6af6560dcc88
spec:
containers:
- env:
- name: APP_COLOR
value: pink
image: kodekloud/webapp-color:v3
imagePullPolicy: IfNotPresent
name: kodekloud-env-color
resources: {}
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
volumeMounts:
- mountPath: /var/run/secrets/kubernetes.io/serviceaccount
name: kube-api-access-xj9jz
readOnly: true
dnsPolicy: ClusterFirst
<SNIP>
Create another copy of this YAML file and modify the definition to change the color fo the App to darkblue.
pradeep@learnk8s$ cp pod-env-variable.yaml pod-env-variable-2.yaml
pradeep@learnk8s$ vi pod-env-variable-2.yaml
The modified version looks like this.
pradeep@learnk8s$ cat pod-env-variable-2.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: "2022-02-15T13:52:07Z"
labels:
run: kodekloud-env-color-2
name: kodekloud-env-color-2
namespace: default
spec:
containers:
- env:
- name: APP_COLOR
value: darkblue
image: kodekloud/webapp-color:v3
imagePullPolicy: IfNotPresent
name: kodekloud-env-color-2
resources: {}
pradeep@learnk8s$ kubectl create -f pod-env-variable-2.yaml
pod/kodekloud-env-color-2 created
pradeep@learnk8s$ kubectl get pods -o wide | grep env
kodekloud-env-color 1/1 Running 0 14m 10.244.1.30 k8s-m02 <none> <none>
kodekloud-env-color-2 1/1 Running 0 16s 10.244.1.31 k8s-m02 <none> <none>
We can verify that this new pod is using the darkblue color.
pradeep@learnk8s$ minikube ssh -p k8s
_ _
_ _ ( ) ( )
___ ___ (_) ___ (_)| |/') _ _ | |_ __
/' _ ` _ `\| |/' _ `\| || , < ( ) ( )| '_`\ /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )( ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)
$ curl 10.244.1.31:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #130f40;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-env-color-2!</h1>
<h2>
Application Version: v3
</h2>
</div>$ curl 10.244.1.31:8080/color
darkblue$
$ curl 10.244.1.31:8080/color
darkblue$
$ exit
logout
